Which lowering blocks to buy and where.

I will be running 15" pathfinders with 205 65 15. I use the truck to haul stuff like rock/gravel/lumber.I was thinking 4" angled blocks in the back and then flip ball joints in front and crank tortions.

Which blocks do you guys recommend? Do you think I should use angled or not? Where is a good place to buy them. Someone before mentioned Autozone but they only had 3" and not angled either.

Thanks for your help guys.